1. Field of the Invention
This invention relates to a process and apparatus for oxygen enriched fossil and synthetic fuel combustion generating controllable, highly luminous, high temperature and high kinetic energy flame. The process and apparatus of this invention provides increased heat transfer to the furnace load, enhanced furnace specific production rate, improved furnace thermal efficiency and reduction in emission of nitrogen oxides. The process and apparatus of this invention provides continuous operation of a fuel cracking chamber when used with regenerative furnaces, such as in the glass making industry.
2. Description of the Prior Art
There have been a number of attempts by a wide variety of techniques to provide combustion of hydrocarbon fuels in a manner to provide improved furnace productivity and increased furnace efficiency, while reducing nitrogen oxides emitted from the furnace. Methods for using oxygen in combustion have been recognized as: addition of oxygen to combustion air; addition of oxygen separately to the combustion zone, as by a lance; and use of a oxygen/fuel burner.
A number of U.S. patents teach staged combustion, principally to obtain lower NO.sub.x emissions. U.S. Pat. No. 4,427,362 teaches a two stage combustion process wherein all of the fuel is mixed with oxygen or oxygen enriched air to provide 45 to 75 percent of the stoichiometric oxygen for combustion and combusted in a first zone with the combustion products being maintained at higher than 2858.degree. F. The combustion products of the first combustion zone are passed to a second combustion zone with 100 to 120 percent stoichiometric air added and combusted at about 2426.degree. to about 3146.degree. F. This patent teaches that the soot and char from the first combustion zone enhances the NO.sub.x reduction rate. U.S. Pat. No. 3,656,878 teaches a high luminosity flame burner wherein all of the combustion air and a portion of hydrocarbon fuel is introduced to a first combustion zone where partial combustion in a diffusion flame produces solid soot particles. It is taught that a free radical promotor may be used and that oxygen is a soot promotor, the free radical promoting effect of oxygen predominating at low concentrations results in increased soot formation. The products of the first combustion zone and fresh hydrocarbon fuel are introduced to the second combustion zone wherein combustion is carried out with a high luminosity flame enhanced by the presence of the soot. U.S. Pat. No. 3,837,788 teaches reduction of NO.sub.x emissions from a two stage combustion process wherein in the first stage fuel is burned with less than about 75 to 80 percent stoichiometry air producing combustion gases at temperatures less than 2700.degree. F., the temperature above which significant amounts of NO.sub.x are produced. The product of the first combustion stage, plus air to support low temperature combustion is passed to a second stage for complete combustion in a specially cooled system so that combustion is carried out at a low temperature, less than that at which NO.sub.x is produced. U.S. Pat. No. 4,505,666 teaches staged two zone combustion for low NO.sub.x emissions wherein about 80 to 95 percent of the combustion air and about 40 to 60 percent of the fuel is supplied to a first combustion zone in a fuel lean mixture and the products of the first combustion zone are supplied to the second combustion zone together with 5 to 20 percent of the air and 40 to 60 percent of the fuel in a fuel-rich mixture. U.S. Pat. No. 4,054,407 teaches a staged catalytic combustion wherein a first stage fuel-rich/air mixture of about 0.2 to 0.5 stoichiometry is combusted in the presence of a catalyst to maintain a low temperature of about 1000.degree. to 1500.degree. F. and a second stage combusts the gaseous products of the first stage with the addition of air to at least stoichiometric amounts, with excess air being used to retain a low temperature. U.S. Pat. No. 3,914,091 teaches two stage catalytic combustion wherein a first stage is carried out under fuel-rich conditions with less than 70 percent stoichiometric air in the presence of a nickel catalyst and a second stage combustion of the product gases of the first stage with additional air to at least stoichiometric amounts is effected to result in low NO.sub.x emissions. Other patents relating to staged combustion processes are U.S. Pat. Nos. 4,405,587; 4,488,866 and 4,403,941.
Regenerative furnaces are widely used in industry, such as in the glass making industry. In regenerative furnaces, combustion oxidizer, typically air or oxygen enriched air is passed through a high temperature regenerator constructed with a thermal energy storage material, such as special shaped refractory brick, called checkers, and is preheated by thermal transfer from the regenerator checkers which previously have been heated by thermal transfer from high temperature furnace exhaust gases. Oxidizer preheating increases flame temperature, enhances heat transfer to the furnace load, increases furnace productivity and improves furnace thermal efficiency. Conventionally, flow of exhaust gases to heat regenerator checkers and flow of oxidizer to be heated by alternate regenerator checkers are switched from one regenerator to the other every 15-20 minutes (cycle time). During such switching period called reversal, the fuel flow is stopped to purge exhaust gases from one regenerator during which the oxidizer cools down the load, furnace, and regenerators until the new fuel and oxidizer flows are established in another regenerator. The reversal amounts to about 3 to about 6 percent of the furnace cycle time and it adversely affects furnace productivity, furnace thermal eficiency, and furnace service life.